The present invention relates to a recording and reproducing apparatus and a variable speed reproducing method using same which are suitable for use in execution of a variable speed reproduction in an IRD (Integrated Receiver Decoder) for recording an MPEG (Motion Picture Experts Group) 2 TS stream onto an HDD (Hard Disk Drive) once.
Digital BS (Broadcast Satellite) broadcasts and digital CS (Communication Satellite) broadcasts have begun to spread. In the digital BS broadcast, video data and audio data are transmitted by an MPEG2 TS stream. To receive such a digital BS broadcast, an apparatus called an IRD is connected to a television receiver. In the IRD, a signal of a desired channel is selected from a reception signal and a video signal and an audio signal are decoded therefrom. The decoded video signal and audio signal are supplied to the TV receiver. A received program of the digital BS broadcast is reproduced by the TV receiver.
As such an IRD of the digital BS broadcast, there is an IRD having an HDD for accumulating the received MPEG2 TS stream. The HDD is used, for example, for accumulating data in a data broadcast or recording a program. When the user has to temporarily leave the TV receiver, the IRD having such an HDD can be used for recording a program which is broadcast while he is away.
Consider, for example, the case where a clerk of a door-to-door parcel delivery service suddenly visits the user when the user is watching a program on the TV receiver. In such a case, since the user has to temporarily leave the TV receiver, he misses the program while he is away. In the case where he is watching a program such as a movie, if he misses a scene in the program, he may lose the context of the scene he missed in the story.
According to the IRD with the HDD, the program is always recorded on the HDD. When the user has to temporarily leave the TV receiver, he operates the TV receiver so as to freeze the received image there and leaves the TV receiver. Even while the user is away from the TV receiver, the received program is recorded onto the HDD.
When the user returns and the frozen state is cancelled, the program recorded on the HDD is reproduced from the position in which the image was frozen. Thus, even if the user has to temporarily leave the TV receiver, he avoids having to miss the program.
On the other hand, the program which is reproduced by the TV receiver when the user returns after he temporarily left the TV receiver as mentioned above is not a program which is actually being broadcast at present, but a program which has already been broadcast a little while before and which has been accumulated on the HDD. If the program which is reproduced from the HDD is fast-forwarded at a speed that is slightly faster than the current time base, the program which is reproduced from the HDD can catch up with the program which is actually being broadcasted at present. By controlling the speed of reproduction from the HDD so that the reproduced program catches up with the program which is actually being broadcast, the program reproduced from the HDD may be switched to the program which is actually being broadcast, and the user is able to watch the program which is actually being broadcast at present from this time point. Such a reproduction is called an overtaking reproduction. The overtaking reproduction is a variable speed reproduction which is executed at a speed that is slightly faster than the normal reproducing speed.
The data which is recorded onto the HDD is an MPEG2 stream. According to the MPEG2 system, three kinds of picture planes called I (Intra) picture, P (Predictive) picture, and B (Bidirectionally Predictive) picture are transmitted. In the I picture, a DCT (Discrete Cosine Transform) encoding is executed by using pixels of the same frame. In the P picture, a motion compensation prediction is executed with reference to the I picture or P picture which has already been encoded, and the difference obtained as a result of such a prediction is encoded. In the B picture, a motion prediction is executed with reference to the I pictures or P pictures before and after the current picture, and the difference obtained as a result of such a prediction is encoded.
In such an MPEG2 encoding, the picture encoded in the picture plane is only the I picture. Therefore, upon variable speed reproduction, generally, only the data of the I picture is extracted from the stream and only this I picture is decoded.
However, if only the I picture is decoded and variable speed reproduction is executed, since the information of the B picture and the P picture existing during the variable speed reproduction is not reproduced, the motion is not smooth and the picture quality deteriorates. In particular, if only the I picture is reproduced and the overtaking reproduction is executed, a clear difference in the picture quality appears between the image obtained before the reproduced program catches up with the program which is being broadcast at present and the image obtained after it has caught up with the current program, so that the user has a strange impression. It is not easy to extract and reproduce only the I picture from the stream which is reproduced from the HDD. A construction for this purpose becomes complicated, resulting in an increase in costs.